1. Field of the Invention
The present invention relates to a method for manufacturing a semiconductor device such as a dynamic random access memory (DRAM) device using hydrogen passivation.
2. Description of the Related Art
In a prior art method for manufacturing a DRAM device of a one-transistor, one-capacitor type, a gate insulating layer is formed on a semiconductor substrate a gate electrode is formed on the gate insulating layer, and an insulating layer is formed on the gate electrode, thus completing a cell transistor.
Next, a capacitor lower electrode, a capacitor dielectric layer, a capacitor upper electrode and an insulating layer are formed, thus completing a cell capacitor.
Further, a first metal wiring layer and its insulating layer are formed, and then, a second metal wiring layer and its passivation layer are formed.
Finally, a hydrogen passivation, which is also called a hydrogen annealing process, is carried out. Thus, hydrogen atoms diffuse and reach the channel region of the cell transistor, so that unsaturated silicon atoms react with hydrogen atoms. As a result, the drain current-to-gate voltage characteristics are improved. That is, an ON-current is increased, a leakage current is decreased, and sub threshold current characteristics are improved. Simultaneously, the first and second metal wiring layers react with their underlying conductive layers by the hydrogen passivation, so that metal alloy such as aluminum alloy is formed therebetween.
This prior art DRAM device will be explained later in detail.
In the above-described prior art method, however, if the capacitor dielectric layer is made of silicon nitride or silicon oxynitride which has a high ability to stop the diffusion of hydrogen atoms therethrough, the hydrogen atoms hardly reach the channel region of the cell transistor. As a result, the improvement of the drain current-to-gate voltage characteristics is insufficient. In order to further increase the amount of hydrogen atoms in the channel region of the cell transistor, if the time period of the hydrogen passivation is further increased, the aluminum of the first and second metal wiring layers is recrystallized to grow the grains thereof. As a result, aluminum hillocks are generated, so that the first and second metal wiring layers are short-circuited.
Note that, in order to enhance the hydrogen passivation, it has been suggested to use a high-pressure hydrogen gas (see JP-A-62-174947). This, however, makes the hydrogen passivation apparatus complex, which increases the manufacturing cost.